2010 Duramax Allison 1000 Transmission Fluid & Filter Service Guide
2010 Duramax Allison 1000 Transmission Fluid Service Guide
Buying a used diesel with 150,000 miles and neglected transmission maintenance requires a careful, specific approach to avoid causing slipping.
The Short Answer (TL;DR)
For a 2010 Duramax LMM with the Allison 1000 6-speed: Do NOT perform a power flush on a neglected unit. Perform a simple drain-and-fill (approx. 7.4 quarts) using TES-295 or TES-668 fluid. You must replace the external red spin-on filter (Part# 29539579) located on the driver's side bell housing. Crucial: Remove the magnet from the old filter, clean it, and install it on the new filter before screwing it on.
The DIY Process Overview
The Allison 1000 is easier to service than most transmissions because of its external filter. You will need a strap wrench, a 15mm socket for the drain plug, and roughly 2-3 gallons of Transynd (or equivalent) fluid.
First, unscrew the external spin-on filter. Check the top of the old filter for a circular magnet; do not throw this away. Wipe the magnet clean and place it over the nipple of the new filter.
Next, pull the drain plug on the pan and let the old fluid drain completely. Reinstall the plug and refill through the dipstick tube. Start the truck, cycle through the gears, and check the level while the fluid is warm.
Why You Should Upgrade While You're In There
Since you are already draining the fluid, this is the ideal time to swap out the factory stamped steel pan for an aftermarket component. The stock pan holds a limited amount of fluid and dissipates heat poorly. Heat is the number one killer of the Allison 1000, especially when towing heavy loads.
Recommended Upgrade: Cast Aluminum Deep Transmission Pan
Installing a deep pan increases fluid capacity by 3-4 quarts and incorporates cooling fins to drop operating temperatures significantly. It also typically includes a magnetic drain plug to capture metal shavings more effectively than stock.
Frequently Asked Questions
Should I change the internal pan filter?
No. On the Allison 1000, the internal filter is a suction screen designed to be changed only during a complete transmission overhaul. Unless you are removing the valve body or rebuilding the unit, leave the internal filter alone.
Is it safe to switch to synthetic fluid at 150k miles?
Yes, provided you do a drain-and-fill rather than a pressurized flush. The "shock" to the system comes from the pressure of a flushing machine dislodging sludge, not the fluid chemistry itself. TES-295 synthetic fluid is backward compatible and superior for thermal stability.
